Bioorienatation of chromosomes during prometaphase is believed to require an activity of two sister kinetochores placed on opposite sides of the chromosome. Recently, we have found that chromosomes can become biooriented and congress onto the metaphase plate even after one kinetochore has been destroyed by laser microirradiation.This indicates that a single kinetochore can interact with microtubles from two opposite poles. A 3-D reconstruction of the kinetochore region of the chromosome after laser irradiation will demonstrate whether microtubules from both opposing spindle poles terminate in the same (single) kinetochore.